Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide two-terminal integrated circuits with time-varying voltage-current characteristics including phase-locked power supplies. Merely by way of example, some embodiments of the invention have been applied to drivers for light emitting diodes (LEDs). But it would be recognized that the invention has a much broader range of applicability.
A single conventional integrated circuit often includes one or more electronic circuits on one or more semiconductor materials (e.g., silicon). The single conventional integrated circuit usually is referred to as an IC, a chip, and/or an IC chip. Additionally, the single conventional integrated circuit often can be made much smaller than a discrete circuit that includes one or more discrete components (e.g., discrete resistor, discrete diode, and/or discrete transistor).
Usually, a conventional IC chip includes three or more terminals that can provide interconnections between the internal circuit(s) of the chip and the external environment. Often, the conventional IC chip uses one terminal to receive a power supply, uses another terminal to provide the ground for a current loop, and uses yet another terminal to provide control for input and/or output.
For example, a conventional LED driver includes a conventional IC chip that operates in the switching-power-supply mode. The conventional IC chip includes three or more terminals (e.g., pins) and uses these terminals to support normal operations. These terminals include a pin to receive the input rectified AC power, another pin to receive the IC power supply, and yet another pin to provide input/output control, and/or to provide the chip ground. The input rectified AC power (e.g., the rectified AC voltage) often periodically becomes zero in magnitude with respect to the chip ground. In another example, the pin for the input rectified AC power is connected to a terminal of an external capacitor, and the other terminal of the external capacitor is connected to the pin for the chip ground. The external capacitor often is needed to provide the power supply to the conventional IC chip when the input rectified AC power (e.g., the rectified AC voltage) periodically becomes zero in magnitude with respect to the chip ground. In yet another example, the conventional IC chip uses the three or more terminals to work with one or more external components (e.g., an inductive winding) outside the chip and convert the received input rectified AC power to a DC power supply for the LED lamps in order to provide a constant LED current under certain control scheme. The use of external capacitor and/or one or more additional pins for the IC chip often raises the bill-of-materials (BOM) cost of the LED driver.
Hence, it is highly desirable to improve techniques for the integrated circuit that, for example, is applicable to an LED drive.